Ionized metal cluster beam systems and methods

Abstract

Ionized metal cluster beam deposition of metal bumps on substrates such as multi-chip modules and integrated circuit chips is enhanced. The present invention discloses wet etching techniques for removing unwanted metal deposited on the substrate around bumps, multiple sources for depositing alloyed (tin-lead) bumps with constant composition, and single or multiple sources for directing a cluster beam through an aperture to deposit metal on a substrate and directing an ion beam at the aperture to remove metal deposited therein.

What is claimed is: 
     
       1. A method of removing metal deposited in a focusing aperture for an ionized metal cluster beam, said method comprising the steps of: generating an ionized metal cluster beam;   providing an aperture holder with a aperture therethrough;   directing the cluster beam at the aperture holder wherein a portion of the cluster beam enters and passes through the aperture whereas another portion of the cluster beam strikes the aperture holder and deposits metal on the aperture holder, and the deposited metal blocks some or all of the aperture;   discontinuing to direct the cluster beam at the aperture;   generating an ion beam;   directing the ion beam at the aperture so that at least some of the deposited metal blocking the aperture is removed;   discontinuing to direct the ion beam at the aperture; and then   directing a portion of the cluster beam at the aperture, thereby preventing the deposited metal from completely blocking the aperture.   
     
     
       2. The method of claim 1 wherein the cluster beam is provided by a liquid metal source. 
     
     
       3. The method of claim 1 wherein the aperture has a diameter in the range of 20 millimeters to 100 millimeters. 
     
     
       4. The method of claim 1 wherein the cluster beam directed at the aperture holder is unfocused and the portion of the cluster beam that passes through the aperture is focused. 
     
     
       5. The method of claim 4, further comprising, directing the portion of the cluster beam which passes through the aperture at the pad area on a substrate, and   depositing metal on the pad area so that a metallic bump is formed on the pad area.   
     
     
       6. The method of claim 1 wherein the cluster beam and the ion beam are generated by separate sources. 
     
     
       7. The method of claim 1 wherein a single source generates the cluster beam and the ion beam. 
     
     
       8. The method of claim 7 wherein the single source is a needle. 
     
     
       9. The method of claim 7 wherein the single source is a capillary. 
     
     
       10. The method of claim 7, further comprising, generating the cluster beam by applying a first voltage to the single source, and   generating the ion beam by applying a second voltage lower than the first voltage to the single source.   
     
     
       11. A system for removing metal deposited in a focusing aperture for an ionized metal cluster beam, the system comprising: an aperture holder with an aperture therethrough;   a source for generating an ionized metal cluster beam capable of directing the cluster beam at the aperture holder so that a portion of the cluster beam enters and passes through the aperture whereas another portion of the cluster beam strikes the aperture holder and deposits metal thereon such that deposited metal blocks some or all of the aperture; and   a source for generating an ion beam capable of directing the ion beam at the aperture so that the ion beam removes at least some of the deposited metal which blocks the aperture, thereby preventing the deposited metal from completely blocking the aperture.   
     
     
       12. The method of claim 11 wherein the cluster beam is provided by a liquid metal source. 
     
     
       13. The system of claim 11 wherein the aperture has a diameter in the range of 20 millimeters to 100 millimeters. 
     
     
       14. The system of claim 11 wherein a single source generates the cluster beam and the ion beam. 
     
     
       15. The system of claim 14 wherein the single source is a needle. 
     
     
       16. The system of claim 14 wherein the single source is a capillary. 
     
     
       17. The system of claim 14, further comprising, a power supply capable of applying a first voltage to the single source which causes the single source to generate the cluster beam, and applying a second voltage lower than the first voltage to the single source which causes the single source to generate the ion beam.   
     
     
       18. The system of claim 14, further comprising, an X-Y stage beneath the aperture holder, the stage being laterally movable relative to the aperture holder and adapted to receive a substrate so that the cluster beam can deposit metal on various areas of the substrate,   an extractor in close proximity to the cluster beam source, and   a shutter between the extractor and the aperture holder capable of being moved in and out of the path of the cluster beam.   
     
     
       19. The system of claim 18, further comprising a computer capable of commanding the operations of: controlling the movement of the X-Y stage,   controlling the movement of the shutter, and   controlling the voltage applied to the source.   
     
     
       20. The system of claim 19 wherein the computer is also capable of commanding the operations of: applying the first voltage to the source so as to generate the cluster beam,   moving the shutter in the path of the cluster beam,   repositioning the X-Y stage,   applying the second voltage to the source so as to generate the ion beam,   reapplying the first voltage to the source so as to generate the cluster beam, and   moving the shutter out of the path of the cluster beam.   
     
     
       21. The system of claim 11 wherein the cluster beam source and the ion beam source are separate sources. 
     
     
       22. The system of claim 21 wherein the aperture holder is movable relative to the cluster beam source and the ion beam source so that the aperture can be positioned in the path of either beam. 
     
     
       23. The system of claim 22 wherein the cluster beam source and the ion beam source are stationary and the aperture holder is movable. 
     
     
       24. The system of claim 23 wherein the aperture holder is rotatable. 
     
     
       25. The system of claim 22 wherein the aperture holder contains a plurality of apertures. 
     
     
       26. The system of claim 25 wherein the plurality of apertures are positionable such that the cluster beam source can direct a portion of the cluster beam at one aperture while the ion beam source can simultaneously direct the ion beam at another aperture. 
     
     
       27. The system of claim 26 wherein the aperture holder includes a disk with an even number of equally spaced apertures therethrough, and portions of the disk between the apertures are able to block the cluster beam. 
     
     
       28. The system of claim 27, further comprising, an X-Y stage beneath the cluster beam source, the stage being laterally movable relative to the cluster beam source and adapted to receive a substrate so that the cluster beam can deposit metal on various areas of the substrate.   
     
     
       29. The system of claim 28, further comprising a computer capable of commanding the operations of: controlling the movement of the X-Y stage,   controlling the positions of the apertures by rotating the aperture holder.   
     
     
       30. The system of claim 29 wherein the computer is also capable of commanding the operations of: rotating the aperture holder so that a first aperture is exposed to the cluster beam and second aperture is exposed to the ion beam,   rotating the aperture holder so that no aperture is exposed to the cluster beam and the aperture holder blocks the cluster beam,   repositioning the X-Y stage, and   rotating the aperture holder so that a third aperture is exposed to the cluster beam and a fourth aperture is exposed to the ion beam.   
     
     
       31. The system of claim 30 wherein the aperture holder rotates half the distance to the next aperture and stops so as to block the cluster beam.